With the rapid development of wooden architecture in China, demand for structural timbers is greatly increased. According to the statistics issued by the Ministry of Housing and Urban-Rural Development, the gap between supply and demand of structural timbers in China was 40 million m3 in 2007. As the wooden structural construction continually develops, and with about 20 million m3 timbers for reconstruction in Sichuan due to the earthquake being taken into account, the gap between supply and demand of structural timbers in China is expected to reach 90 million m3 in 2010. According to the officials of the Canadian federal government, Canada has built about 300 units and plans to build another 9000 units of wooden structure houses in mainland China. It is estimated that about 15,000 units per year of the wooden structure houses will be built in China within the next five years, which brings enormous market potential for structural wood. If small-diameter plantation wood is made into solid wood composite panels or composited with bamboo so as to be made into ultra-thick composite panels by means of the technological breakthrough, in order to replace the large diameter high-quality wood, which is very important in alleviating the tense wood supply, and also brings a wider market prospect.
At present, solid wood composites panels mainly comprise such two categories of products as blackboard and multi-layer solid wood composite plywood. Blockboard is a kind of special plywood, and the manufacture comprises the following steps, firstly battens splice together to form core board, then a layer of veneer covers respectively on the upper and lower surface of the core board to form slab, last glue press is carried out on the slab. The core board is usually composed of spliced board or wood lattice structural panel, and the preparation is as follows, the log is sawed into battens with the width of 20 to 100 mm and thickness of 1 to 5 mm, then such strips are combined together to form the core board. Said method to prepare core board has such shortages as the large kerf losses while sawing the log, and the low wood utilization ratio. Based on the current situation that fast-growing plantation wood is dominated in commercial timbers of China, and the plantation wood usually contains the following defects, the small diameter class, the low density, the loose structure, the low strength, and so on. If plantation wood is directly sawed to be used as dimension lumbers, it will be with the following problems, the more scraps, and high unqualified ratio of dimension lumbers caused by knot, and juvenile wood, which will lead to the low utilization ratio. Additionally, because the wood strips which are combined together to form blockboard, are jointed by using glue joint in transverse, which lead to that the transverse MOR of the core board mainly depends on the joint strength of adhesive, so the blockboard usually can't meet the national standard because of the low transverse strength (see Zou Lin-lin, Lv Bin, Yang Na. The Analysis with the Development Status and Quality Problem of Block Board in China, Forestry Machinery & Woodworking Equipment, 2006, 34 (5):4-6).
Either from the view of the content and the scope of the research, or from the view of the depth of the research, the research level of bamboo/wood composite in China is in a world-leading position. According to incomplete statistics, in China, there are nearly thousand of various processing enterprises of bamboo-based panel and several dozens of products, the products are widely used in automobile compartment floor, container floor, construction of cement template, floor, decorative materials, furniture, and so on. (Zhang Ying-he, Thinking on the development of Bamboo-based Panel, Wood Processing Machinery, 2004). If small diameter wood is processed into veneers, and using the veneers alone or combined with bamboo so as to produce structural plywood or laminated veneer lumber, then the wood utilization ratio will be greatly increased.
In the existing technology, the multi-layer solid wood plywood or wood/bamboo composite plywood are produced as follows, the log, such as fast-growing plantation wood, is made into veneers with the thickness of 1 to 3 mm, the veneer is then used as core layer, and the plywood, laminated veneer lumber, or solid wood composites and bamboo/wood composites are produced after the following procedure, drying, gluing, assembling, hot pressing, and so on. The veneer used in such composite panels is thin, during the production of composite panels with the same thickness, the thinner veneer, the more glue layers are, and the adhesives used are more. As the adhesives used are generally thermosetting aldehyde adhesives, such as phenolic-aldehyde resin and urea-formaldehyde resin, and so on, thus more adhesives will cause the increase of the formaldehyde emission and the costs.
The patent CN01133469.X has provided a multi-layer solid wood composite panel, wherein a 3-ply plywood is made of veneers with the thickness of 4 to 10 mm, and said plywood is used as core layer, the said composite panel is produced after sanding, and a surface layer overlaying the upper and lower surface of said core layer. Such composite panel made of thick veneers, can solve the problems caused by foregoing thin veneers and large amounts of glue used. However, it is difficult to peel veneers with the thickness more than 5 mm using traditional peeling equipment and it is mainly due to that, the veneer is originally circular arc in the wood segment, when wood is peeled into veneers, the veneers are level during peeling, and successively reverse bended. The result is that, compressive (σ1) stress is produced on the surface of the veneer, and tensile (σ2) stress is produced on the back of the veneer:
            σ      1        =                  E        ·        S                    2        ⁢                                  ⁢                  ρ          1                      ,            σ      2        =                  E        ·        S                    2        ⁢                                  ⁢                  ρ          2                    wherein, ρ1 represents curvature radius of veneer in initial state (mm), ρ2 represents curvature radius of veneer while reverse bending (mm), E represents elastic modulus along the grain of the wood (MPa), and S represents veneer thickness (mm) (see Wood-based Panel Technology, p 46, China Forestry Publishing House, Hua yu-kun). It can be seen from the formula that, the smaller the log diameter, the larger the thickness of the veneer, the greater the inner stress is, and it is easier to produce warping and deformation during the drying of the veneer (even bending and deformation are caused, as shown in FIG. 1). When the stress is larger than the transverse tensile or compressive strength, the veneer will crack, the above defects will seriously affect the wood outturn percentage and the subsequent processing procedures, such as glue spreading procedure and assembling procedure. Secondly, when veneer with such structure is used as core board, because of the excessive veneer stress, it is easy for the made composite panels to produce warping and deformation; moreover, the secondary overlaying process is used, the overlaying procedure is added.
Furthermore, hot-pressing forming method is generally used in the forming of the existing composite panels. Additionally, both bamboo and wood are poor conductors of heat, the difficulty of using hot-pressing to produce thick panels is greater, so the thickness of existing panels is generally smaller than 30 mm.